In a number of applications, various users of electronic systems have found it desirable to interact with the electronic systems through a display, e.g., a computer monitor, a television, a personal digital assistant (PDA) and automated teller, in order to input information into the system. Thus, a number of designers have utilized various technologies in an attempt to improve touch sensitive input devices, such as touch sensitive screens and digitizer pads. Various types of these input devices have been designed using, for example, capacitive, resistive, infrared, surface acoustic wave (SAW) and guided acoustic wave (GAW) technologies.
Most touch sensitive screens implementing capacitive technology have been realized by fusing a transparent thin film conductive coating onto a glass surface. A low voltage AC field has then been applied to and distributed across the conductive coating such that when a user's finger made contact with a surface of the screen it capacitively coupled with the AC field drawing a small amount of current to the point of contact. In such screens, the current flow from each corner of the conductive coating is proportional to the distance to the user's finger and the ratios of the current flows are measured by a control unit to determine where the user touched the screen.
Typically, resistive touch sensitive screens have utilized a contacting member, e.g., a stylus, to form a momentary connection between two semi-flexible conductive layers. A control unit then determines where the contacting member touched the screen by sensing a change in voltage. Infrared technologies have implemented control units that detect a change in infrared light propagation, initiated when a user touches a touch screen, to determine where the user touched the screen.
Touch pads implementing SAW technology have generally included a glass panel with transducers that transmit and receive surface waves over the face of the touch pad. When a finger or other object touched the surface of the screen, a portion of the energy of the wave was absorbed at that location, which could then be determined by a control unit, based upon the presence of interference patterns in the acoustic wave. Typical characteristics of input devices implementing the above-referenced technologies are set forth below in Table 1.
TABLE 1CAPACITIVERESISTIVEINFRAREDGAWSAWResolution (PPI)>250>200815033Z-axis?NoNoNoYesYesAmbient LightUnaffectedUnaffectedVariesUnaffectedUnaffectedActivationTactileTactileProximityTactileTactileParallax?NoNoYesNoNoResponse Time5–15 ms5–10 ms18–40 ms18–50 ms20–50 msTransmissivity85–92%65–80%100%92%92%Sensor Reliability20 M touches/point35 M touches/point138K hrs MTBFUnlimited50 M touches/pointIntegrationInvasive or non-Invasive. OpticalInvasive or non-Invasive. OpticalInvasive. Opticalinvasive.bonding required.invasive.bonding required.bonding required.Stylus TypeRequires conductiveNo stylus limitation.No stylus limitation.Requires soft,Requires soft,stylus. Cannotenergy absorbingenergy absorbingdetect gloved finger.stylus.stylus.Sensor DriftSubject to drift.Subject to drift.Not subject to drift.Not subject to drift.Not subject to drift.Requires repetitiveRequires repetitivecalibration.calibration.DurabilityConductive layerSensor isNot susceptible toDifficult to scratch.Difficult to scratch.subject to wear.susceptible toscratching, noGlass overlay isGlass overlay isscratches andoverlay, solid state.breakable.breakable.abrasions.Dust/DirtAccumulationNot affected by dustWill operate withNot affected by dustWill operate withResistanceaffects performance.and dirt.dust and dirt.and dirt.dust and dirt.ExcessiveExcessiveaccumulation mayaccumulation mayaffect performance.affect performance.
The various technologies have relative advantages and disadvantages depending upon the specific application. None of the currently available technologies are generally suitable for automotive display applications, which require minimal interaction time between driver and touch sensitive input device, allowing the driver to keep his/her eyes on the road and drive in a safe manner. Further, in general, most automotive display applications require only a limited number of touch sensitive “spots,” as opposed to devices such as personal digital assistants that allow high resolution touch sensitive response. In addition, the driver may be wearing gloves, which affects the ability of currently available touch screens to properly resolve a point of contact on a display's surface.
Many stand-alone switches are used in controlling automotive features and functions. Typically, these switches have dedicated functions, as indicated by artwork on the switches, and the switches are illuminated by small lamps or light pipes from a common lamp in the case of multiple switch pods. In general, such switches are not wired directly to the function that they are controlling, but instead serve as human interfaces to send appropriate control messages across a vehicle system bus from which information is extracted and used to actuate an appropriate function.
Light emitting structures, such as organic light emitting diodes (OLEDs) and polymer light emitting diodes (PLEDs), have been built on a variety of opaque and transparent substrates. In general, OLEDs and PLEDs, which may be designed to emit a variety of colors, may be built on rigid substrates, e.g., glass, or flexible substrates, e.g., a flexible polymer.
The LCD Keyswitch Division of Rapid Technology Interfaces Ltd. has developed a pushbutton key switch that integrates a liquid crystal display (LCD), which is backlit with four pairs of light emitting diodes (LEDs), and an application specific integrated circuit (ASIC) internal controller chip. The LCD can display text and graphics, as well as animation, and is directed to input systems for telecommunications, CTI, point-of-sale, military and industrial control panels, audio/video production equipment, and radio and TV studio controls. The display can be changed dynamically when a function of the key switch is changed. In general, the key switch implements four connections for supply power, ground, a clock and a data line and two additional connections serve as switch contacts. However, the above-described key switch utilizes a relatively complicated bulky structure that is unwieldy for many applications.
What is needed for automotive and other commercial applications is a retaskable switch-indicator unit that is durable, compact and relatively inexpensive to manufacture. It would also be desirable if the unit minimized electromagnetic interference (EMI), so as to not adversely affect other electronic systems of the motor vehicle.